Assessment of tribological performance and thermal stability of metakaolin-based geopolymer composites reinforced with high TiO2 concentration.

This study investigates the influence of titanium dioxide (TiO2) incorporation (0-50 wt.%) on the structural, thermal, and tribological properties of metakaolin-based geopolymer composites (GPCs). The bulk density of the composites increased progressively from 1.81 g/cm3 for the control sample to 2.86 g/cm3 at 50 wt.% TiO2, while apparent porosity decreased from 33.47 to 23.48%. Water absorption was correspondingly reduced from 8.43 to 5.34% after 24 h immersion, confirming the pore-filling effect of TiO2. XRD and FTIR analyses indicated the coexistence of amorphous aluminosilicate gel, residual quartz, and anatase reflections, with Ti-O and Ti-O-Si vibrations confirming the physical embedding of TiO2 without disrupting the geopolymeric framework. SEM micrographs revealed that higher TiO2 content led to a denser morphology with fewer pores, confirming densification. DSC/TGA revealed that TiO2 addition enhanced stability and reduced low-temperature mass loss. Pin-on-disc testing showed that adding 40 wt.% TiO2 significantly improved tribological performance, reducing the wear rate from 3.45 × 10-5 to 1.12 × 10-5 mm3/N m and the steady-state friction coefficient from 0.36 to 0.29. These results confirm the dual role of TiO2 as a microstructural densifier and a reinforcing agent, enabling the development of geopolymer composites with enhanced durability, thermal stability, and wear resistance suitable for high-performance structural applications in extreme environments.